1. Field of Technology
The disclosure relates generally to systems and methods of radiography. More particularly, the disclosure relates to systems and methods of perming underwater radiography, including at significant depths subsea.
2. Background Information
The basic principles of radiography are well-understood. Positioning an object of interest between a radiation source and a detector causes a portion of the electromagnetic radiation emitted from the source to be absorbed by the object and a portion to pass through the object, due to variations in density and composition of the object of interest. Electromagnetic radiation that is not absorbed by the object of interest may be captured by the detector, forming an image on the detector. The resulting image may then be processed and enhanced by various means. Different types of sources may be used in radiography, including X-ray producing X-ray tubes and gamma ray producing radioactive sources. Radioactive sources may be naturally occurring such as radium, mesothorium and the like, or artificial such as cobalt-60, iridium-192 and the like. Detectors may comprise film sensitive to electromagnetic radiation, phosphor coated imaging plates, or digital image capture devices such as flat panel detectors and high intensity line scan solid state detectors.
A very common application of radiography is in the medical field where it is used to allow physicians to visually observe the condition of bones and other features internal to a patient's body. Various types of electromagnetic radiation may be used in radiography, including x-rays and gamma rays, depending on the application. Because of its ability to create representations of the internal components of an object, industrial radiography has been employed in the analysis and non-destructive testing (NDT) of engineered structures, machines and other man-made products. For instance, industrial radiography may be used in testing and inspecting plate metal, pipe wall and welds on pressure vessels and conduits. Further, various techniques may be used in industrial radiography, including single wall exposure (SWE) techniques where the radiation source is placed internal of the object of interest, and double wall exposure (DWE) techniques where the source is placed externally on one side of the object of interest, with the imaging plate placed on the opposing side.
Underwater pipelines, cables, and products and structures associated with underwater oil and gas wells may require analysis and testing, specifically NDT. These objects may be located at the sea floor, which may be 5,000-7,000 feet or more below the surface, wherein the hydrostatic pressure of the water may exceed 2,000 pounds per square inch (PSI). Operating in such an environment may present unique challenges in which to attempt radiography, and may render certain conventional radiography equipment ineffective. For instance, ionizing radiation may be absorbed by the water, lengthening the necessary exposure time to form the radiographic image. Further, carrying out radiography at such depths requires that the underwater radiology system components be provided proximal to the sea floor and positioned by deep diving, remotely operated vehicles (ROVs) controlled by an operator at the surface. Not only may conventional radiography systems and components be unable to withstand the extreme pressures encountered in a subsea environment, but they may be too fragile to be handled by the manipulating arms of an ROV. Further, accurately controlling an ROV from substantial distances, and using an ROV to position and operate components of conventional radiography systems, may be impractical in many instances.
Accordingly, there remains a need in the art for apparatus, systems, and methods for conducting subsea radiography operations to image subsea equipment. Such apparatus, systems, and methods would be particularly well-received if they were suitable for use by ROVs in relatively deep see environments.